Generally, halogens are known as environmental toxins, and therefore industrial materials are made progressively halogen-free. In particular, there has been an increased demand for halogen-free materials in the field of office automation equipments, and most housings of personal computers, printers and the like are made progressively halogen-free.
Some material fields independently create halogen-free standards; for example, the Japan Electronics Packaging Circuits Association defines a printed circuit board containing “900 ppm or less of bromine, 900 ppm or less of chlorine, and 1500 ppm in total of bromine and chlorine” as halogen-free (JPCA-ES01-2003).
Meanwhile, expanded polyurethane foam is more difficult to be made flame-retardant than other resin materials, and therefore halogen compounds and halogen-containing phosphoric acid ester compounds that are highly effective as flame retardants have been used so far. With the current preference for halogen-free materials, however, the tendency has been to voluntarily shift to halogen-free flame retardants.
In order to be halogen-free, a flame retardant is required to have a halogen content of an added resin material comparable to or lower than the above-mentioned definition of the halogen-free printed circuit board.
In the meantime, phosphoric acid esters are known as useful chemical substances in a wide range of fields in the chemical industry as additives for resins such as flame retardants and plasticizers and as materials or intermediates of pharmaceutical products and the like.
In particular, it is known that a phosphoric acid ester having a cyclic alkylene skeleton delivers superior performance as a flame retardant because of its characteristic structure. For example, Japanese Unexamined Patent Publication No. HEI 11(1999)-181428 (Patent Document 1) discloses that a phosphoric acid ester having a phosphorinane skeleton is useful as a flame retardant for polyurethane resin.
In addition, phosphorous acid esters having a cyclic alkylene skeleton are generally useful chemical substances in a wide range of fields in the chemical industry, being widely used not only as intermediates of the above-mentioned phosphoric acid esters but also as stabilizers of resins and various kinds of compounds.
For example, Japanese Unexamined Patent Publication No. HEI 5(1993)-239264 (Patent Document 2) discloses that 5,5-dimethyl-2-nonylphenoxy-1,3,2-dioxaphosphorinane can be used as a stabilizer of cellulose ester resin and effectively prevent discoloration of the polymer and deterioration of physical properties due to a lowered degree of polymerization of the ester resin.
Cyclic alkylene phosphorohalidites are used as intermediates in production of the above-mentioned phosphoric acid esters or phosphorous acid esters having a cyclic alkylene skeleton and generally obtained through a reaction between a phosphorus trihalide and an alkylene glycol compound.
For example, Japanese Unexamined Patent Publication No. HEI 2(1990)-273688 (Patent Document 3) discloses that phosphorus trichloride is added to and reacted with neopentyl glycol under ice cooling to obtain 5,5-dimethyl-2-chloro-1,3,2-dioxaphosphorinane.
The pamphlet of WO 2006/049010 (Patent Document 4) discloses a method for producing a phosphonate having an alcoholic hydroxy group by addition reaction of a phosphite having two substituents with a carbonyl compound in the presence of a nitrogen-containing basic compound and a metal halide; and the pamphlet of WO 2006/049011 (Patent Document 5) discloses a method for producing a phosphorus compound having a phosphate-phosphonate bond by subjecting a phosphonate having an alcoholic hydroxy group and a di-substituted phosphorohalidite to a dehydrohalogenation reaction in the presence of a nitrogen-containing basic compound, and oxidizing the resulting reaction product with hydrogen peroxide, for example.